1. Field of the Invention
This invention relates to a process for the preparation of monoaryl phosphonates, useful as antiwear additives, a method for reducing wear between moving metal surfaces in contact with a lubricant composition containing an effective amount of said antiwear additive and to lubricant compositions comprising a major proportion of an oil of lubricating viscosity or grease prepared therefrom containing a minor amount of said antiwear additive.
2. Description of the Prior Art
Monoaryl phosphonates have heretofore been prepared, as described in U.S. Pat. No. 3,019,249, by the reaction of phosphorous acid with triaryl phosphites in accordance with the general equation: ##STR1## One disadvantage to this method is that monoaryl phosphonates so produced are difficult to purify and the product is usually contaminated with one of the reactants. Also, phosphorous acid is hygroscopic, and accidentally-absorbed water in the phosphorous acid reactant will hydrolyze part of the product monoaryl phosphonate to phosphorous acid and the corresponding phenol.
Another method for preparing monoaryl phosphonates is described in Houben Weyl, "Methoden der Organischen Chemie," edited by Eugen Muller, Georg Thieme Verlag, Stuttgart, 1964, Vol. 12, part 2, page 6. This method involves hydrolysis of the corresponding aryl-phosphorodichloridite in accordance with the following general equation: ##STR2## As stated in Houben Weyl, the product is unstable in the reaction medium and usually hydrolyzes extensively before it can be isolated.
The method in accordance with this invention provides a general catalytic synthesis of monoaryl phosphonates which may be accomplished in the absence of water or other hydroxylic impurities and which affords a substantially pure monoaryl phosphonate product which is virtually free of other phosphorous-containing impurities and which is capable of easy separation from the catalyst employed.